This invention relates to metal halide high-intensity discharae lamps, and more particularly, to metal halide lamps operable from a constant wattage-type mercury ballast.
A metal halide lamp that may be started on a high pressure mercury vapor lamp ballast is disclosed in U.S. Pat. No. 3,900,761 dated Aug. 19, 1975 issued to Freese et al. A resistor and a diode are connected between the starter electrode and the adjacent main electrode and a second resistor is connected in circuit between the starter electrode and its connector to an external power supply.
A high-intensity discharge lamp utilizing a starter electrode voltage doubling circuit is disclosed in U.S. Pat. No. 3,982,154 dated Sept. 21, 1976, issued to Mize et al. The voltage doubling circuit comprises a diode and a mica-dielectric capacitor which is electrically interposed between an inlead into the jacket and the frame side rod and forms an integral structural part of the frame and supports the arc tube. The starter electrode is resistively connected to the side rod to facilitate starting and the arrangement maintains a positive DC bias on the frame which reduces electrolysis of sodium through the arc tube walls.
An arc discharge lamp designed to prevent electrolysis is disclosed in U.S. Pat. No. 3,619,711 dated Nov. 9, 1971 issued to Robert W. Freese, Jr. The arc tube of the discharge lamp has two main electrodes and a starter electrode adjacent one of them, the starting electrode being electrically connected to the adjacent electrode through a rectifying device, such as a diode, external of the arc tube. The polarity of the rectifier is such as to permit the starter electrode to obtain a voltage positive with respect to the adjacent electrode, but to substantially prevent negative voltage therebetween.
Another discharge lamp designed to prevent electrolysis is disclosed in U.S. Pat. No. 3,619,710 dated Nov. 9, 1971 issued to John F. Waymouth. This patent discloses that the starter electrode is electrically connected to the other main electrode through a thermally operative switch and a second resistor. In normal operation, the switch opens after lamp ignition to isolate the starter electrode from the circuit of the other main electrode to place the starter electrode at substantially the same potential as the adjacent main electrode.